Home Automation Part 4 – Using the Home Phone Grid For 1-Wire

byJustin GehringonJune 26, 2013

Today’s goal was to get the 2 sensors I had working last night, working in other rooms.

My goal for this project is to make the sensors small, unobtrusive, and ideally as cheap as possible. To that end, I decided I wanted to basically crimp them right into the RJ-11 connector. I started there, and this is what they ended up looking like:

All in all, very happy with how the sensors are turning out. So much so that I ordered 10 more DS18B20’s so I can load them into every phone jack in the house. The phone jacks make an ideal candidate for the wiring for a few reasons:

We don’t use any land-line phones (but even if we did, there’s enough extra cable that I could have 1 phone line and the sensors if I really wanted to.

All the phone lines should be in parallel, which is what is needed for wiring these things together.

There’s on average 1 jack per room (which is what I want to record).

The lines are already in the walls (big time saver).

The cabling is meant for low(er) voltage applications

I made the decision to actually use 3 wires going back to the computer (as opposed to just 2). This will allow me to change the circuit in the future from parasitic power to non-parasitic power without having to rebuild all my sensors. If you want to read more about the 2 versions of the circuit that I’m playing with, read the first half of this article.

The first thing I did was take a trip outside to customer demark point for the houses phone lines. There I disconnected the phone service completely from my house (just unplugged the cables for the 2 lines that were previously installed). Even though my service was already stopped, these lines needed to be physically disconnected. While they were still plugged in, my home phone network was grounded and possibly even still getting power from the phone company (not sure, didn’t take the time to measure, just know it had to be disconnected for my circuit to only be “my circuit”).

From there, I went upstairs and started plugging in my components. I made an adapter to go from my 1-wire serial interface to an RJ-11 (making note to get the pins right). I then plugged my adapter into the wall, and took my sensor to another room in hopes that it would again just magically work.

It didn’t.

I tried another room.

That didn’t work either.

So off came the plates from the wall jacks. Much to my surprise I discovered 2 things that I find far to often in the low voltage world. First, they hadn’t wired all 4 pins of the phone jacks… just the 2 middle pins (all that is needed for a single line). While this isn’t entirely uncommon, it really is someone deciding to be lazy. There’s no reason NOT to wire all 4 pins properly other than time. Since I had decided to use 3 wires for this project, this meant I would need to go to every jack and wire in the extra set of wires that were just sitting there.

The second thing that I discovered in *some* of the jacks, is that for some reason, the person installing them got a little color blind (or something… I’m not sure). In any case, they started mixing and matching colors… And while it was *probably* functionally correct (I’m not positive on that), it was definitely not a normal thing to do… And became highly frustrating when trying to figure out if the pin mapping at each jack was correct because suddenly red wasn’t red, and yellow wasn’t yellow. In any case, I redid any I saw that were wrong as well… and so far, so good.

I presently am able to use my sensors in any room on the bedroom level. I’ll do the main level and basement hopefully tomorrow night. I’m also hoping my new Thermostat will arrive tomorrow. If it does, I might even go so far as to writing some simple programming that will allow me to display the temp of the other 2 sensors on thermostat’s screen (it has that ability). However, that’s going to be hard if I don’t get a Linux box setup for this. So much to do… The screen thing might have to wait til the weekend… We shall see.